“In fact, Buddhism, which had flourished in Bharat for 1600 years, suddenly vanished almost completely as soon as Muslims became masters of Delhi and started raiding the plains of Ganga.” Citation needed?
1) https://en.wikipedia.org/wiki/Decline_of_Buddhism_in_the_Ind... - From 986 CE, the Turks started raiding northwest India from Afghanistan, plundering western India early in the eleventh century. Forced conversions to Islam were made, and Buddhist images smashed, due to the Islamic dislike of idolatry. Indeed in India, the Islamic term for an 'idol' became 'budd'. — Peter Harvey, An Introduction to Buddhism ... According to William Johnston, hundreds of Buddhist monasteries and shrines were destroyed, Buddhist texts were burnt by the armies, monks and nuns killed during the 12th and 13th centuries in the Gangetic plains region. The Islamic invasions plundered wealth and destroyed Buddhist images ... The decline of Buddhism in the Indian subcontinent coincides with the spread of Islam in that part of the world, especially due to the Islamic invasions that occurred in the late 12th century. See sections "Turkic Invasions" and "Decline under Islamic Rule".
Buddhism was the tranquilizing death of India. You can argue that Islamic invaders would have conquered India anyways - but with Buddhism they rarely even had to fight!
Their puzzlement is even captured in several journals where they could range for hundreds of miles and loot/burn with little to no resistance. And do it once again a few years later!
There is a stronger argument to be made that it was because of the establishment of Buddhism as the de-facto state philosophy/religion/practice in North/Northwest part of India that the Islamic invaders could conquer India. Buddhism for all its intellectual/ethical/moral strengths was not a pragmatic religion. It ignored the realities of Life in favour of higher ideals in a context ill-suited to its survival and hence paid the price at the hands of barbaric muslim invaders. This happened through the elevation of Ahimsa into an all-encompassing tenet of state policy which severely sapped the Martial Spirit of the population and thus could offer no resistance to invaders bent on genocide. Prior to Buddhism (and Jainism) while Ahimsa was considered one of the central pillars of Hinduism its limitations in the practical world were acknowledged and Kings were expected to protect by force if necessary, those practicing Ahimsa as a way of life. With this gone, North/Northwest India was easy prey to barbaric muslim invaders who did not play by the same rules.